Switching circuit on power supply for magnetic disk recording device

ABSTRACT

According to one embodiment, there is provided a disk device including a head, a disk, a first motor, and a first circuit. The disk has a recording surface. The first motor causes the head to seek along the recording surface. The first circuit can switch between a first state and a second state. The first state is a state where a current path of the first motor is electrically cut off from a first electricity storage unit. The second state is a state where the current path of the first motor is electrically connected to the first electricity storage unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2017-254051, filed on Dec. 28, 2017; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a disk device and aninformation processing apparatus.

BACKGROUND

Disk devices having motors realize predetermined control operation bysupplying electric power for driving to the motors. In this case, it isdesired that the power usage efficiency of the disk device be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating schematically the configuration of adisk device according to an embodiment;

FIG. 2 is a diagram illustrating the circuit configuration of the diskdevice according to the embodiment;

FIG. 3 is a diagram illustrating the configuration of circuitry relatedto a VCM and SPM in the embodiment;

FIG. 4 is a flow chart illustrating in outline the operation of the diskdevice according to the embodiment;

FIG. 5 is a flow chart illustrating a seek mode selection process in theembodiment;

FIG. 6 is a state transition diagram illustrating the transition of acharge-discharge seek mode in the embodiment;

FIG. 7 is a state transition diagram illustrating the transition of acharge-discharge mode in the embodiment;

FIG. 8 is a flow chart illustrating a seek execution process in theembodiment;

FIG. 9 is a flow chart illustrating a speed control process in theembodiment;

FIG. 10 is a flow chart illustrating a switching process in theembodiment;

FIG. 11 is a flow chart illustrating a pre-decision process in theembodiment;

FIG. 12 is a waveform chart illustrating a seek execution process in acharge-discharge off seek mode in the embodiment;

FIG. 13 is a waveform chart illustrating a seek execution process in acharge seek mode in the embodiment;

FIG. 14 is a waveform chart illustrating the charging current in acharge mode in the embodiment;

FIG. 15 is a diagram illustrating schematically the configuration of aninformation processing apparatus including disk devices according to amodified example of the embodiment;

FIG. 16 is a diagram illustrating schematically the configuration of thedisk device according to the modified example of the embodiment; and

FIG. 17 is a diagram illustrating the configuration of circuitry relatedto a VCM and SPM in the modified example of the embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, there is provided a disk deviceincluding a head, a disk, a first motor, and a first circuit. The diskhas a recording surface. The first motor causes the head to seek alongthe recording surface. The first circuit can switch between a firststate where a current path of the first motor is electrically cut offfrom a first electricity storage unit and a second state where thecurrent path of the first motor is electrically connected to the firstelectricity storage unit.

Exemplary embodiments of a disk device will be explained below in detailwith reference to the accompanying drawings. The present invention isnot limited to the following embodiments.

(Embodiment)

A disk device according to an embodiment will be described. The diskdevice includes a plurality of motors and supplies electric power fordriving to each of the motors, thereby realizing predetermined controloperation. For example, a disk device 100 is configured as shown inFIG. 1. FIG. 1 is a diagram illustrating schematically the configurationof the disk device 100.

The disk device 100 is, for example, a hard disk device, is connected toa host 200 via a communication line 201 to be communicative, andfunctions as an external storage medium of the host 200. For example,the communication line 201 may be a serial communication line, and thehost 200 may be a personal computer, or the communication line 201 maybe a wired and/or wireless network, and the host 200 may be a server.The disk device 100 may be configured such that power can be suppliedfrom the host 200 via a power line group 202. The power line group 202includes a power line 2021 and a power line 2022.

The disk device 100 comprises a chassis 1, a disk 2, a spindle motor(SPM) 3, a spindle 5, a head MH, an actuator arm AM, a voice coil motor(VCM) 4, and a control unit 10. The control unit 10 controls thecomponents and, for example, supplies electric power for driving to eachof the SPM (second motor) 3 and VCM (first motor) 4, thereby realizingpredetermined control operation. The control unit 10 includes a headcontrol unit 20, a motor control unit 30, a read write channel 40, and ahard disk control unit 50.

The chassis 1 rotatably supports the disk 2 via the spindle 5. The disk2 is a disk-shaped recording medium (e.g., a magnetic disk) on which avariety of information can be recorded. The disk 2 has multiple tracksconcentric with the spindle 5 as the center, or one spiral track. Oneach track, multiple data areas and servo areas are provided alternatelyin a circumferential direction. The chassis 1 slidably supports theactuator arm AM via the VCM 4. The actuator arm AM holds the head MH atits tip on the opposite side from the VCM 4.

The head MH is moved to seek as the actuator arm AM slides, so as toperform a write operation of writing data onto the disk 2 and a readoperation of reading data from the disk 2. The head MH includes a writehead WH by which to perform the write operation and a read head RH bywhich to perform the read operation. The head MH is held at the tip ofthe actuator arm AM and moves in a down track direction above therecording surface 2 a of the disk 2 with being kept floating slightlyabove the recording surface 2 a of the disk 2 by lift force generated bythe rotation of the disk 2.

The head control unit 20 controls write operations and/or readoperations by the head MH. The head control unit 20 includes a writesignal control unit 21 and a read signal detecting unit 22. The writesignal control unit 21 generates a write current according to a writesignal received from the hard disk control unit 50 via the read writechannel 40 to supply to the write head WH. The read signal detectingunit 22 generates a read signal according to a read current receivedfrom the read head RH to supply to the hard disk control unit 50 via theread write channel 40.

The motor control unit 30 controls the supply of power to each motor.The motor control unit 30 includes an SPM drive circuit 31 and a VCMdrive circuit 32.

The SPM drive circuit 31 supplies electric power for driving (e.g.,drive current) to the SPM 3 to control the rotation of the SPM 3. TheSPM 3 rotates the disk 2 with the spindle 5 as the center using electricpower for driving received from the SPM drive circuit 31. By this means,the head MH moves in a down track direction above the recording surface2 a of the disk 2.

The VCM drive circuit 32 supplies electric power for driving (e.g.,drive voltage) to the VCM 4 to control the drive of the VCM 4. The VCM 4causes the actuator arm AM to slide in a direction along the recordingsurface 2 a using electric power for driving received from the controlunit 10 so as to make the head MH seek along the recording surface 2 a.By this means, the VCM 4 makes the head MH move in a cross trackdirection so as to change tracks on the disk 2 on which to perform awrite operation and/or a read operation.

The read write channel 40 performs data transfer between the headcontrol unit 20 and the hard disk control unit 50. The read writechannel 40 converts a signal (data, a servo signal, or the like) read bythe read head RH to a data format that the host 200 deals with andconverts data outputted from the host 200 to a signal format for thewrite head WH to write.

The hard disk control unit 50 controls each part of the disk device 100according to firmware and performs interface operations for the host200. When receiving a write request and data from the host 200 via thecommunication line 201, the hard disk control unit 50, in response tothe write request, controls writing the data onto the disk 2 via theread write channel 40, head control unit 20, and head MH. When receivinga read request from the host 200 via the communication line 201, thehard disk control unit 50, in response to the read request, reads datafrom the disk 2 via the head MH, head control unit 20, and read writechannel 40 and transmits to the host 200 via the communication line 201.

The hard disk control unit 50 includes a controller control unit 51 anda servo control unit 52. The controller control unit 51 includes asector access processing unit 511, a reordering processing unit 512, anda command queue 513. The servo control unit 52 includes a trackingprocessing unit 521 and a seek processing unit 522.

The seek processing unit 522 includes a state estimating unit 5221 and asubtracter 5222 shown in FIG. 2. FIG. 2 is a diagram illustrating thecircuit configuration of the disk device 100. The state estimating unit5221 receives a current specifying value I_(tgt_d) from the VCM drivecircuit 32 as shown in FIG. 2 and obtains an estimated position p_(esti)and an estimated velocity v_(esti) of the head MH based on the currentspecifying value I_(tgt_d) by using an observer. The state estimatingunit 5221 takes the difference in the estimated velocity v_(esti)between samples to obtain an estimated acceleration a_(esti). The seekprocessing unit 522 obtains the current position (head position) p ofthe head MH based on a servo signal read from servo areas of the disk 2and takes the difference between the current position p and theestimated position p_(esti) with use of the subtracter 5222 to obtain anestimated position error p_(err). The seek processing unit 522 correctsstate estimated values (the estimated position p_(esti), estimatedvelocity v_(esti), and estimated acceleration a_(esti)) of the head MHso that the estimated position error p_(err) comes closer to zero,changes the current specifying value I_(tgt_d) according to thecorrected state estimated values, and supplies the changed currentspecifying value I_(tgt_d) as a current specifying value I_(tgt_d) 321to the VCM drive circuit 32.

In the VCM drive circuit 32, the current specifying value I_(tgt_d) 321(a digital signal) is DA-converted into a current specifying signalI_(tgt_a) (an analog signal) by a DA converter 322; a VCM current I_(v)is converted into a VCM signal I_(v_s) by a sense resistance R_(s) 325;and the VCM signal I_(v_s) is subtracted from the current specifyingsignal I_(tgt_a) by a subtracter 323 to generate an error signal I_(e)to be supplied to a current amplification amplifier 324. The currentamplification amplifier 324 receives a power supply voltage V_(sup_V2)from a V2 transformer 66 and, using the power supply voltage V_(sup_V2),performs filtering on the error signal I_(e) by a filter circuit 3241 togenerate an error signal I_(ef) and to generate a drive voltage V_(amp)according to the error signal I_(ef). The current amplificationamplifier 324 can adjust the response time of VCM current control byadjusting coefficients of the filter circuit 3241. The currentamplification amplifier 324 supplies the drive voltage V_(amp) to theVCM 4. This causes a VCM current I_(v) according to the currentspecifying value I_(tgt_d) to flow through the VCM 4, so that the VCM 4causes the actuator arm AM to slide in a direction along the recordingsurface 2 a to make the head MH seek along the recording surface 2 a.

At this time, in the VCM 4, although the magnitude of the VCM currentI_(v) may vary, back electro-motive force (BEMF) to prevent thevariation of the VCM current I_(v) may be generated, so that a backelectromotive voltage V_(bemf) according to the moving velocity v of theactuator arm AM may be generated. The back electromotive voltageV_(bemf) can be expressed by the following equation 1.V _(bemf) =K _(f) ×V  Eq. 1

In equation 1, K_(f) is a current force constant when it is taken as anapproximation that the head MH moves in translation in a radialdirection of the disk 2. Electrical energy according to this backelectromotive voltage V_(bemf) in seek operation, if retained in the VCM4, may become thermal energy due to the resistance component of itscurrent path, resulting in an increase in the temperature of the VCM 4.It is desired that the disk device 100 effectively utilize thiselectrical energy to improve the power usage efficiency.

Accordingly, in the present embodiment, by configuring the disk device100 such that a current path of the VCM 4 can be electrically connectedto an electricity storage unit 13, the electricity storage unit 13 canbe charged with a current according to the back electromotive voltageV_(bemf) of the VCM 4 in the disk device 100 to improve the power usageefficiency.

That is, in the disk device 100, during a constant speed period in aseek time period when seek operation is performed, the current path ofthe VCM 4 and the electricity storage unit 13 are connected to beconductive, so that the electricity storage unit 13 is charged withelectricity using the back electromotive voltage V_(bemf) of the VCM 4.While charging the electricity storage unit 13 with electricity isrepeated several times, the amount of power stored in the electricitystorage unit 13 is monitored, and, when the amount of power in theelectricity storage unit 13 exceeds a threshold, the SPM 3, VCM 4, ICs11, 12, and the like are driven using power in the electricity storageunit 13. By this means, electrical energy according to the backelectromotive voltage V_(bemf) of the VCM 4 can be effectively utilized,so that the total power consumption in the disk device 100 can bereduced.

Specifically, as shown in FIGS. 1 and 2, the control unit 10 furtherincludes the ICs 11, 12, the electricity storage unit 13, an electricitystorage unit 14, a V1 power supply terminal 15, and a V2 power supplyterminal 16. The hard disk control unit 50 further includes acharge-discharge control unit 55, a charging circuit (first circuit) 56,a charging circuit (second circuit) 57, a discharging circuit (thirdcircuit) 58, a discharging circuit (fourth circuit) 59, a power supplycontrol unit 61, a V1 power supply selector 62, a V2 power supplyselector 63, a V1 transformer 64, a V3 transformer 65, and a V2transformer 66.

In FIG. 2, the charging circuit 56 can switch between a first state anda second state. The first state is a state where the current path of theVCM 4 is electrically cut off from the electricity storage unit 13. Thesecond state is a state where the current path of the VCM 4 iselectrically connected to the electricity storage unit 13. The chargingcircuit 56 has a switch SW1, one end of the switch SW1 beingelectrically connected to the current path of the VCM 4, the other endof the switch SW1 being electrically connected to the electricitystorage unit 13. According to a control signal received from thecharge-discharge control unit 55, the charging circuit 56 turns off theswitch SW1 to switch to the first state and turns on the switch SW1 toswitch to the second state.

For example, the charging circuit 56 switches from the first state tothe second state during a seek time period when the head MH is made toseek. That is, the seek time period contains an acceleration period, aconstant speed period, and a deceleration period. The accelerationperiod is a period when the speed of the head MH is accelerated and is aperiod when the absolute value of the acceleration of the head MHexceeds a first threshold. The constant speed period is subsequent tothe acceleration period, is a period when the speed of the head MH canbe controlled to be almost constant, and is a period when the absolutevalue of the acceleration of the head MH is smaller than the firstthreshold. The deceleration period is subsequent to the constant speedperiod, is a period when the speed of the head MH is decelerated and isa period when the absolute value of the acceleration of the head MHexceeds the first threshold. At a first timing corresponding toswitching from the acceleration period to the constant speed period, thecharging circuit 56 switches from the first state to the second state.Thus, during the constant speed period, the charging circuit 56 can makethe VCM current I_(v) from the VCM 4 as a charging current I_(c) flowinto the electricity storage unit 13 to charge the electricity storageunit 13. At a second timing corresponding to switching from the constantspeed period to the deceleration period, the charging circuit 56switches from the second state to the first state. Thus, the chargingcircuit 56 can finish charging the electricity storage unit 13 withelectricity immediately before switching from the constant speed periodto the deceleration period.

The charging circuit 56 is configured as shown in, e.g., FIG. 3. FIG. 3is a diagram illustrating the configuration of circuitry related to theVCM 4 and SPM 3, and related circuitry. The switch SW1 of the chargingcircuit 56 has a P-channel transistor Tr21 and an N-channel transistorTr22. The transistors Tr21 and Tr22 form a transfer gate, the sources ofthe two being connected in common to form one end of the switch SW1, thedrains of the two being connected in common to form the other end of theswitch SW1. The charge-discharge control unit 55 supplies a controlsignal of a high (H) level to the gate of the transistor Tr21 and acontrol signal of a low (L) level to the gate of the transistor Tr22,thereby turning off the switch SW1. The charge-discharge control unit 55performs at least one of supplying the control signal of the L level tothe gate of the transistor Tr21 and supplying the control signal of theH level to the gate of the transistor Tr22, thereby turning on theswitch SW1.

When the charging circuit 56 switches to the second state, theelectricity storage unit 13 is charged with a current (the VCM currentI_(v)) according to the back electromotive voltage V_(bemf) of the VCM4. The electricity storage unit 13 has a battery 131, and one end of thebattery 131 is electrically connected to the charging circuit 56. Theother end of the battery 131 may be electrically connected to thecurrent path of the VCM 4 as shown in FIG. 3, or may be connected toground potential. The battery 131 is configured to be able to storeelectrical charge and is, for example, an electric double layercapacitor, an electrolytic capacitor, a ceramic capacitor, a secondarybattery (e.g., a lithium-ion secondary battery, nickel-hydrogen storagecell), or the like.

The discharging circuit 58 shown in FIG. 2 can switch between a fifthstate and a sixth state. The fifth state is a state where theelectricity storage unit 13 is electrically cut off from the V1 powersupply selector 62 and/or the V2 power supply selector 63. The sixthstate is a state where the electricity storage unit 13 is electricallyconnected to the V1 power supply selector 62 and/or the V2 power supplyselector 63. The discharging circuit 58 has switches SW3 and SW4, oneend of the switch SW3 being electrically connected to the electricitystorage unit 13, the other end of the switch SW3 being electricallyconnected to the V1 power supply selector 62, one end of the switch SW4being electrically connected to the electricity storage unit 13, and theother end of the switch SW4 being electrically connected to the V2 powersupply selector 63. According to a control signal received from thecharge-discharge control unit 55, the discharging circuit 58 turns offthe switch SW3 and/or switch SW4 to switch to the fifth state and turnson the switch SW3 and/or switch SW4 to switch to the sixth state.

For example, when power stored in the electricity storage unit 13 comesgreater than or equal to a second threshold, the discharging circuit 58switches from the fifth state to the sixth state. The second thresholdcan be determined, for example, considering at least one of powernecessary for driving the ICs 11, 12, power necessary for driving theVCM 4 (seek operation), and power necessary for driving the SPM 3(rotational operation).

The V2 transformer 66 shown in FIG. 3 can be regarded equivalently as avoltage source E supplying the power supply voltage V_(sup_V2), and theVCM drive circuit 32 can be equivalently formed of an H bridge circuit.The VCM drive circuit 32 has P-channel transistors Tr11, Tr13 andN-channel transistors Tr12, Tr14. The transistors Tr11, Tr13 have theirsources connected in common to the higher voltage side of the voltagesource E, and the transistors Tr12, Tr14 have their sources connected incommon to the lower voltage side of the voltage source E. Thetransistors Tr11, Tr12 have their drains connected in common to one endof the current path of the VCM 4, and the transistors Tr13, Tr14 havetheir drains connected in common to the other end of the current path ofthe VCM 4. A resistance R_(v) and an inductor Lv are connected in seriesbetween the one end and the other end of the current path of the VCM 4.

For example, during the seek time period, the charge-discharge controlunit 55 controls the charging circuit 55 not to perform charging in theacceleration period and the deceleration period but to perform chargingin the constant speed period so as to charge the electricity storageunit 13. Variation in acceleration caused by switching during theconstant speed period in the seek time period is small, so that theinfluence on VCM vibration excitation is small. While electricityremains stored, VCM control and driving ICs are executed by theelectricity storage unit 13 discharging.

The charge-discharge control unit 55 can control a charge-dischargemode, thereby controlling whether the charging circuit 56 charges andwhether the discharging circuit 58 discharges. When the charge-dischargemode is a charge-discharge off mode, because the current conduction ofthe transistors Tr21, Tr22 are set to be off, normal VCM application isexecuted. That is, when the seek direction is forward (from the outercircumference to the inner circumference of the disk 2), the transistorsare controlled as shown in Table 1, and when the seek direction isreverse (from the inner circumference to the outer circumference of thedisk 2), the transistors are controlled as shown in Table 2.

TABLE 1 SEEK DIRECTION: Forward (FROM OUTER CIRCUMFERENCE TO INNERCIRCUMFERENCE) CONSTANT CONSTANT DECEL- SPEED ACCELERATION SPEED ERATIONCHARGING Tr₁₁ Off Off On Off Tr₁₂ On On Off Off Tr₁₃ On On Off Off Tr₁₄Off Off On Off Tr₂₁ Off Off Off On Tr₂₂ Off Off Off Off

TABLE 2 SEEK DIRECTION: Reverse (FROM INNER CIRCUMFERENCE TO OUTERCIRCUMFERENCE) CONSTANT CONSTANT DECEL- SPEED ACCELERATION SPEED ERATIONCHARGING Tr₁₁ On On Off Off Tr₁₂ Off Off On Off Tr₁₃ Off Off On Off Tr₁₄On On Off Off Tr₂₁ Off Off Off Off Tr₂₂ Off Off Off On

When the charge-discharge mode is a charge mode, all the transistorsTr11, Tr12, Tr13, Tr14 of the H bridge circuit are turned off in currentconduction, and simultaneously the voltage source E is set to 0 V. Thepolarity of the back electromotive voltage is determined according towhether a seek is done toward the disk inner circumference (forwardseek) or a seek is done toward the disk outer circumference (reverseseek). As shown in Tables 1 and 2, either the transistor Tr21 or Tr22 isturned on with the other being turned off according to the polarity ofthe back electromotive voltage, so that electricity can be passedthrough the electricity storage unit 13 (the battery 131). Theelectricity storage unit 13 may be able to determine the polarityinternally and charge.

When the SPM 3 shown in FIG. 2 is an alternating-current motor, thecharging circuit 57 has a switch SW2 and a rectifying circuit 571. Therectifying circuit 571 is connected to the current path of the SPM 3 andrectifies an alternating current according to the back electromotivevoltage of the SPM 3. The charging circuit 57 can switch between a thirdstate and a fourth state. The third state is a state where therectifying circuit 571 is electrically cut off from the electricitystorage unit 14. The fourth state is a state where the rectifyingcircuit 571 is electrically connected to the electricity storage unit14. In the charging circuit 57, one end of the switch SW2 iselectrically connected to the rectifying circuit 571, and the other endof the switch SW2 is electrically connected to the electricity storageunit 14. According to a control signal received from thecharge-discharge control unit 55, the charging circuit 57 turns off theswitch SW2 to switch to the third state and turns on the switch SW2 toswitch to the fourth state.

For example, the charging circuit 57 switches from the third state tothe fourth state in an idling period or a power loss protection (PLP)period. The idling period is a period when a sector access processingunit 511 is not currently executing a command and when also no commandis queued in the command queue 513. The PLP period is a period when apower supply disconnection has been detected in the disk device 100(e.g., the supply of power from the host 200 via the power line group202 and the V1 power supply terminal 15 and/or V2 power supply terminal16 has been cut off) and when data temporarily stored in a volatilememory (e.g., IC 11 shown in FIG. 1) is to be written into the disk 2and/or a nonvolatile memory (e.g., IC 12 shown in FIG. 1) to be saved.

The charging circuit 57 is configured as shown in, e.g., FIG. 3. Theswitch SW2 of the charging circuit 57 has a P-channel transistor Tr41and an N-channel transistors Tr42. The transistors Tr41 and Tr42 form atransfer gate, the sources of the two being connected in common to formone end of the switch SW2, the drains of the two being connected incommon to form the other end of the switch SW2. The charge-dischargecontrol unit 55 supplies a control signal of the H level to the gate ofthe transistor Tr41 and a control signal of the L level to the gate ofthe transistor Tr42, thereby turning off the switch SW2. Thecharge-discharge control unit 55 performs at least one of supplying thecontrol signal of the L level to the gate of the transistor Tr41 andsupplying the control signal of the H level to the gate of thetransistor Tr42, thereby turning on the switch SW2.

When the charging circuit 57 switches to the fourth state, theelectricity storage unit 14 is charged with a current according to theback electromotive voltage of the SPM 3 and rectified by the rectifyingcircuit 571. The electricity storage unit 14 has a battery 141, and oneend of the battery 141 is electrically connected to the charging circuit57. The other end of the battery 141 may be electrically connected tothe reference potential side of the rectifying circuit 571 as shown inFIG. 3, or may be connected to ground potential. The battery 141 isconfigured to be able to store electrical charge and is, for example, anelectric double layer capacitor, an electrolytic capacitor, a ceramiccapacitor, a secondary battery (e.g., a lithium-ion secondary battery,nickel-hydrogen storage cell), or the like.

The discharging circuit 59 can switch between a seventh state and aneighth state. The seventh state is a state where the electricity storageunit 14 is electrically cut off from the V1 power supply selector 52and/or the V2 power supply selector 53. The eighth state is a statewhere the electricity storage unit 14 is electrically connected to theV1 power supply selector 62 and/or the V2 power supply selector 53. Thedischarging circuit 59 has switches SW5 and SW6, one end of the switchSW5 being electrically connected to the electricity storage unit 14, theother end of the switch SW5 being electrically connected to the V1 powersupply selector 62, one end of the switch SW6 being electricallyconnected to the electricity storage unit 14, and the other end of theswitch SW6 being electrically connected to the V2 power supply selector63. According to a control signal received from the charge-dischargecontrol unit 55, the discharging circuit 59 turns off the switch SW5and/or switch SW6 to switch to the seventh state and turns on the switchSW5 and/or switch SW6 to switch to the eighth state.

For example, the discharging circuit 59 switches from the seventh stateto the eighth state during the PLP period.

It should be noted that the SPM drive circuit 31 can be equivalentlyformed of an inverter circuit (circuit reversely convertingdirect-current power into alternating-current power). The SPM drivecircuit 31 has N-channel transistors Tr31 to Tr36 and freewheel diodesD31 to D36. The transistors Tr31 to Tr33 have their drains connected incommon to the higher voltage side of the voltage source E, and thetransistors Tr34 to Tr35 have their sources connected in common to thelower voltage side of the voltage source E. The SPM drive circuit 31reversely converts, for example, direct-current power into three-phasealternating-current power. The SPM 3 has inductors L1 to L3corresponding to the three phases. The source of the transistor Tr31 andthe drain of the transistor Tr34 are connected in common to one end ofthe inductor L1; the source of the transistor Tr32 and the drain of thetransistor Tr35 are connected in common to one end of the inductor L2;and the source of the transistor Tr33 and the drain of the transistorTr36 are connected in common to one end of the inductor L3. In thecurrent path of the SPM 3, the other ends of the inductors L1 to L3 areconnected to ground potential. In the rectifying circuit 571, threeserial connections of two diodes D corresponding to the three phases areconnected in parallel between the reference-side line and ahigher-voltage-side line, and each of the inductors L1 to L3corresponding to the three phases is electrically connected to the nodebetween the two diodes D of one of the serial connections.

A voltage (e.g., 5 V) to be a power supply voltage V1 can be steadilysupplied from the host 200 via the power line 2102 to the V1 powersupply terminal 15 shown in FIG. 1. The V1 power supply selector 62shown in FIG. 2, according to a control signal received from the powersupply control unit 61, selects a voltage to be adopted as the powersupply voltage V1 from among a voltage V_(inp_V1) received via the V1power supply terminal 15, a voltage V_(inp_b_V1) supplied from theelectricity storage unit 13 via the discharging circuit 58, and avoltage V_(inp_c_V1) supplied from the electricity storage unit 14 viathe discharging circuit 59. The V1 power supply selector 62 supplies theselected voltage V_(sel_V1), V_(sel_V3) to the V1 transformer 64 and V3transformer 65 respectively. The V1 transformer 64 transforms thevoltage V_(sel_V1) into an internal power supply voltage V_(sup_V1) forV1 (e.g., 5 V) operation to supply to the IC 11. The V3 transformer 65transforms the voltage V_(sel_V3) into an internal power supply voltageV_(sup_V3) for V3 (e.g., 3 V) operation to supply to the IC 12. The V1transformer 64 and the V3 transformer 65 can transform into the internalpower supply voltages V_(sup_V1) and V_(sup_V3) as constant voltages,using a regulator, a charge pump, or the like.

A voltage (e.g., 12 V) to be a power supply voltage V2 can be steadilysupplied from the host 200 via the power line 2022 to the V2 powersupply terminal 16 shown in FIG. 1. The V2 power supply selector 63shown in FIG. 2, according to a control signal received from the powersupply control unit 61, selects a voltage to be adopted as the powersupply voltage V2 from among a voltage V_(inp_V2) received via the V2power supply terminal 16, a voltage V_(inp_b_V2) supplied from theelectricity storage unit 13 via the discharging circuit 58, and avoltage V_(inp_c_V2) supplied from the electricity storage unit 14 viathe discharging circuit 59. The V2 power supply selector 63 supplies theselected voltage V_(sel_V2) to the V2 transformer 66. The V2 transformer66 transforms the voltage V_(sel_V2) into an internal power supplyvoltage V_(sup_V2) for V2 (e.g., 12 V) operation to supply to the SPMdrive circuit 31 and the VCM drive circuit 32. The V2 transformer 66 cantransform into the internal power supply voltage V_(sup_V2) as aconstant voltage, using a regulator, a charge pump, or the like.

Next, sector access command processing in the disk device 100 will bedescribed using FIG. 4. FIG. 4 is a flow chart illustrating in outlinethe operation of the disk device 100 in the sector access commandprocessing.

When receiving a sector access request (e.g., a write request, readrequest, or the like) from the host 200, the disk device 100 has thecontroller control unit 51 execute a command reordering process todetermine the access destination (access sector) (S1). For example, thecontroller control unit 51 generates a command according to the sectoraccess request (e.g., a write command according to a write request, aread command according to a read request, or the like) to enqueue intothe command queue 513. The reordering processing unit 512 selects thecommand whose access time is the shortest from among multiple commandsqueued in the command queue 513 in the command reordering process tostart executing it. The controller control unit 51 determines the accessdestination (access sector according to the address specified by thecommand) according to the selected command and generates a seek requestaccording to the access destination to notify to the servo control unit52 (S2). At this time, the controller control unit 51 notifies thetarget sector and an expected access time contained in the seek requestto the servo control unit 52.

The servo control unit 52 waits until receiving the seek request(containing the target sector and an expected access time) from thecontroller control unit 51 (No at S3) and, when receiving the seekrequest (Yes at S3), performs a seek mode selection process (S10).

In the seek mode selection process (S10), processing shown in, e.g.,FIG. 5 is performed. FIG. 5 is a flow chart illustrating the seek modeselection process.

At a seek start, the servo control unit 52 performs as a seek modeinitializing process the initialization of a charge-discharge seek mode,initialization of a charge-discharge mode, initialization of aconstant-speed start decision flag, and initialization of aconstant-speed end pre-decision flag (S11). The charge-discharge seekmode is set to be a mode on a per seek operation basis as shown in FIG.6. FIG. 6 is a state transition diagram illustrating the transition ofthe charge-discharge seek mode. The charge-discharge seek mode isinitially set to be a charge-discharge off seek mode. Thecharge-discharge mode is set to be a mode on a per control sample basis(e.g., per sample of servo control) as shown in FIG. 7. FIG. 7 is astate transition diagram illustrating the transition of thecharge-discharge mode. The charge-discharge mode is initially set to bea charge-discharge off mode. The constant-speed start decision flag is aflag which is to be set in order to cause the decision to startconstant-speed control and is initially set to be low. Theconstant-speed end pre-decision flag is a flag which is to be set inorder to cause the decision before the finish timing to endconstant-speed control and is initially set to be low. That is, in theseek mode initializing process, the servo control unit 52 sets thecharge-discharge seek mode to the charge-discharge off seek mode, thecharge-discharge mode to the charge-discharge off mode, theconstant-speed start decision flag to be low, and the constant-speed endpre-decision flag to be low.

Referring back to FIG. 5, the servo control unit 52 performs a chargedstate measuring process (S12). If a discharge seek is possible withpower currently stored in the electricity storage unit 13 on the basisof the calculation from the power consumption of a normal seek, adischarge seek possible flag is set.

If the discharge seek possible flag is set (Yes at S13), the servocontrol unit 52 makes the charge-discharge seek mode and thecharge-discharge mode transition to update as shown in FIGS. 6 and 7(S14). That is, the servo control unit 52 sets the charge-discharge seekmode to be the discharge seek mode and the charge-discharge mode to bethe discharge mode.

Referring back to FIG. 5, the servo control unit 52 selects a currentJIT seek type in a current JIT seek type selection process (S15). TheJIT seek is a seek to reach a target sector exactly and is generally lowin current level. Or it selects a seek profile containing a constantspeed period. As a result, the effect of reducing the power consumptionand vibration is produced.

If the discharge seek possible flag is not set (No at S13), the servocontrol unit 52 performs a charge JIT seek type selection process (S16).In this, a seek profile that is a combination of charging and JIT isdetermined. For example, if a charge seek in a rotation wait time ispossible, the charge-discharge seek mode is made to transition from thecharge-discharge off seek mode to the charge seek mode as shown in FIG.6. If the rotation wait time has an enough margin, a JIT seek may beperformed to make the seek further slow. Or, with some seek distances,if the use of an existing JIT seek without charging is advantageous interms of power consumption, the charge-discharge seek mode may be keptbeing the charge-discharge off seek mode, without switching to thecharge seek mode.

Referring back to FIG. 4, the servo control unit 52 selects a seek modein the seek mode selection process (S10) and then performs a seekexecution process (S20).

In the seek execution process (S20), the servo control unit 52 performsthe seek execution process as shown in FIG. 8. FIG. 8 is a flow chartillustrating the seek execution process. The servo control unit 52performs acceleration control (S21) and performs speed control during atleast the deceleration period in the seek time period (S30).

In the speed control (S30), the servo control unit 52 performs the speedcontrol process as shown in FIG. 9. FIG. 9 is a flow chart illustratingthe speed control process. The servo control unit 52 calculates theposition of the head MH using the servo signal read from servo areas ofthe disk 2 (S31) and performs a state estimating process to estimate thestate (an estimated position p_(esti), an estimated velocity v_(esti),and an estimated acceleration a_(esti)) of the head MH using a stateobserver (S32). The servo control unit 52 takes the difference betweenthe current position p calculated at S31 and the estimated Positionp_(esti) estimated at S32 to obtain an estimated position error p_(err)and corrects state estimated values (the estimated position p_(esti),estimated velocity v_(esti), and estimated acceleration a_(esti)) of thehead MH so that the estimated position error p_(err) comes closer tozero and determines the current specifying value I_(tgt_d) according tothe corrected state estimated values (S33). The servo control unit 52supplies the current specifying value I_(tgt_d) determined at S33 as acurrent specifying value I_(tgt_d) 321 to the VCM drive circuit 32.Thus, VCM current application processing is performed which causes theVCM current I_(v) according to the current specifying value I_(tgt_d) toflow through the VCM 4 (S34). Then the servo control unit 52 performs aswitching process (S40).

In the switching process (S40), the servo control unit 52 performs theswitching process as shown in FIG. 10. FIG. 10 is a flow chartillustrating the switching process. The servo control unit 52 ascertainsthe charge-discharge seek mode and, if the charge-discharge seek mode isnot the charge seek mode (“the others” at S41), ends the process. If thecharge-discharge seek mode is the charge seek mode (“charge seek mode”at S41), the servo control unit 52 ascertains the constant-speed startdecision flag and, if the constant-speed start decision flag is high(High at S42), ends the process because the speed is determined to beconstant in a constant-speed determination process, so that thereafterthe constant-speed determination process need not be performed. If theconstant-speed start decision flag is low (Low at S42), the servocontrol unit 52 performs the constant-speed determination process todecide on a timing in a constant speed period at which to start charging(S43). For example, if the absolute value of the acceleration of thehead MH exceeds the first threshold, the servo control unit 52 can allowthe constant-speed start decision flag to remain low and, if theabsolute value of the acceleration of the head MH is less than or equalto the first threshold, can change the constant-speed start decisionflag from low to high.

The servo control unit 52 ascertains the constant-speed start decisionflag and, if the constant-speed start decision flag remains low (Low atS44), ends the process on the basis that charging need not be performed.If the constant-speed start decision flag is high (High at S44), theservo control unit 52 makes the charge-discharge mode transition fromthe charge-discharge off mode to the charge mode to set on the basisthat charging can be started because the speed is constant (S45).

Referring back to FIG. 9, after performing the switching process (S40),the servo control unit 52 performs a pre-decision process (S50).

In the pre-decision process (S50), the servo control unit 52 performsthe pre-decision process as shown in FIG. 11. FIG. 11 is a flow chartillustrating the pre-decision process. The servo control unit 52ascertains the charge-discharge seek mode and, if the charge-dischargeseek mode is not the charge seek mode (“the others” at S51), ends theprocess. If the charge-discharge seek mode is the charge seek mode(“charge seek mode” at S51), the servo control unit 52 ascertains theconstant-speed start decision flag and, if the constant-speed startdecision flag is low (Low at S52), ends the process on the basis thatcharging is not being performed. If the constant-speed start decisionflag is high (High at S52), the servo control unit 52 ascertains theconstant-speed end pre-decision flag and, if the constant-speed endpre-decision flag is high (High at S53), ends the process because theprocess later than the constant-speed end pre-decision is unnecessary.If the constant-speed end pre-decision flag is low (Low at S53), theservo control unit 52 performs the constant-speed end pre-determination(S54). That is, the servo control unit 52 obtains the difference betweenthe current position p of the head MH and the target position p_(tgt) asa remaining distance d_(r) and allows the constant-speed endpre-decision flag to remain low until the absolute value of theremaining distance d_(r) becomes less than a threshold and, when theabsolute value of the remaining distance d_(r) becomes less than thethreshold, can change the constant-speed end pre-decision flag from lowto high.

The servo control unit 52 ascertains the constant-speed end pre-decisionflag and, if the constant-speed end pre-decision flag is low (Low atS55), ends the process and, if the constant-speed end pre-decision flagis high (High at S55), makes the charge-discharge mode transition fromthe charge mode to the charge-discharge off mode to set on the basisthat the timing at which to end charging has been reached (S56).

Referring back to FIG. 9, the servo control unit 52 performs aconstant-speed end decision process (S35) and, if determining that thetiming at which to switch from the constant speed period to thedeceleration period has been reached, ends the process. By this means,speed control (S30) finishes.

Referring back to FIG. 8, after the speed control (S30) finishes (afterthe seek time period ends), the servo control unit 52 performs positioncontrol (S22).

For example, if the charge-discharge seek mode is set to be thecharge-discharge off seek mode (normal seek mode), the servo controlunit 52 performs control as shown in FIG. 12. FIG. 12 is a waveformchart illustrating a seek execution process in the charge-discharge offseek mode.

When the seek time period Tsk starts, the servo control unit 52 performsacceleration control, speed control, and position control sequentially.That is, the servo control unit 52 performs acceleration control in theacceleration period Tup, constant-speed control for speed control in theconstant speed period Tcs, and deceleration control for speed control inthe deceleration period Tdn. After the seek time period Tsk ends, theservo control unit 52 performs position control.

At timing t1, acceleration control starts. In acceleration control,applied voltage V_(amp) across the opposite ends of the VCM 4 iscontrolled to accelerate the velocity v of the head MH by the VCM 4. Ifthere is a restriction on the head velocity upper limit v_(t), when thevelocity v of the head MH reaches the head velocity upper limit v_(t)(e.g., timing t2), the servo control unit 52 switches to constant-speedcontrol (i.e., switches from the acceleration period Tup to the constantspeed period Tcs). At this time, because the back electromotive voltageis developed, applied voltage V_(amp)=V_(rev) to cancel out the backelectromotive voltage is applied in order to maintain speed. In order toreach the target track to stop, the servo control unit 52 checks a tableof velocity against the remaining distance d_(r) for each sample and, ifconditions are satisfied (e.g., timing t3), switches from constant-speedcontrol to deceleration control (i.e., switches from the constant speedperiod Tcs to the deceleration period Tdn). When seek operation finishesat timing t4, the servo control unit 52 performs the position control ofthe head MH using the servo signal read from servo areas of the disk 2.

Or, for example, if the charge-discharge seek mode is set to be thecharge seek mode, the servo control unit 52 performs control as shown inFIG. 13. FIG. 13 is a waveform chart illustrating a seek executionprocess in the charge seek mode.

The servo control unit 52 initializes the constant-speed start decisionflag and the constant-speed end pre-decision flag (set the flags to below) at a seek start. If the charge-discharge seek mode is set to be thecharge seek mode, when the head velocity becomes constant, that is, whenthe head acceleration comes close to zero, the servo control unit 52switches the charge-discharge mode from the charge-discharge off mode tothe charge mode. At switching during the constant speed period Tcs inthe seek time period Tsk, variation in acceleration is small, so thatthe influence on VCM vibration excitation is small. After switching fromacceleration control to speed control for constant speed, switching thecharge-discharge mode is performed.

For example, using the estimated acceleration a_(esti) of the stateobserver and an acceleration threshold th_(acc), if |a_(esti)|<th_(acc)is satisfied, it is determined that the speed is constant, and theconstant-speed start decision flag is changed from low to high. Whendetermining that the speed is constant (at timing t11 when theconstant-speed start decision flag becomes high), the servo control unit52 changes a charge mode switch flag from low to high and makes thecharge-discharge mode transition from the charge-discharge off mode tothe charge mode to set. After this, the servo control unit 52 maintainsthe constant-speed start decision flag high. When put in the chargemode, electricity from power supply does not pass through the VCM 4, andbecause a back electromotive voltage is mainly developed across the VCM4, the head velocity v gradually decreases. Hence, in the charge seekmode, the seek time is longer than in the charge off seek mode (normalseek).

Thus, as shown in FIG. 14, at timing t11, a charging current Ic due to aback electromotive voltage V_(BEMF_C) of the VCM 4 starts flowing intothe electricity storage unit 13 so that charging the electricity storageunit 13 starts. FIG. 14 is a waveform chart illustrating the chargingcurrent in the charge mode.

The servo control unit 52 makes a decision for switching from the chargemode to the charge off mode at timing t12 before timing t3 at which toswitch to deceleration control as shown in FIG. 13. This decision ismade in the constant-speed end pre-decision process. As opposed to anormal mechanism for switching from constant speed control todeceleration control, a mechanism which makes a decision earlier isadopted. For example, when using a table of velocity against theremaining distance d_(r), the servo control unit 52 multiplies the dataseries of the remaining distance by a correction coefficient k_(d) of avalue greater than one so as to determine that the constant speed is toend at a timing earlier than switching to deceleration control and tochange the constant-speed end pre-decision flag from low to high. Whendetermining that the constant speed is to end (at timing t12 when theconstant-speed end pre-decision flag becomes high), the servo controlunit 52 changes a charge off mode switch flag from low to high and makesthe charge-discharge mode transition from the charge mode to thecharge-discharge off mode to set. After this, the servo control unit 52maintains the constant-speed end pre-decision flag high.

Thus, as shown in FIG. 14, at timing t12, the charging current Ic due tothe back electromotive voltage V_(BEMF_C) of the VCM 4 finishes flowinginto the electricity storage unit 13 so that charging the electricitystorage unit 13 finishes.

Referring back to FIG. 4, after the seek execution process (S20)finishes, the servo control unit 52 notifies seek completion to thecontroller control unit 51 (S4). The controller control unit 51 waitsuntil seek completion is notified by the servo control unit 52 (No atS5), and when seek completion is notified by the servo control unit 52(Yes at S5), finishes the sector access command processing.

As such, in the present embodiment, the disk device 100 is configuredsuch that the current path of the VCM 4 can be electrically connected tothe electricity storage unit 13. Thus, the electricity storage unit 13can be charged with a current according to the back electromotivevoltage V_(bemf) of the VCM 4 in the disk device 100. Further, whilecharging the electricity storage unit 13 with electricity is repeatedseveral times, the amount of power stored in the electricity storageunit 13 is monitored, and, when the amount of power in the electricitystorage unit 13 exceeds a threshold, the SPM 3, VCM 4, ICs 11, 12, andthe like can be driven using power in the electricity storage unit 13.By this means, electrical energy according to the back electromotivevoltage V_(bemf) of the VCM 4 can be effectively utilized, so that thetotal power consumption in the disk device 100 can be reduced.

Note that although, being put in the charge seek mode, the seek time islonger than in the charge-discharge off seek mode (normal seek) as shownin FIGS. 13 and 14, the disk device 100 has a function of determiningwhether a charge seek is to be performed according to the rotation waittime in random access, so that the random access performance is notimpaired.

Instead of the electricity storage unit 13 being provided in the diskdevice 100 (see FIG. 1), an electricity storage unit 13 a may beprovided in a host 200 a as shown in FIG. 15. FIG. 15 is a diagramillustrating schematically the configuration of an informationprocessing apparatus 300 a including disk devices 100 a-1 to 100 a-N.That is, the information processing apparatus 300 a includes the host200 a and the multiple disk devices 100 a-1 to 100 a-N, where N is aninteger of two or greater. The host 200 a has the electricity storageunit 13 a configured to be shared by the multiple disk devices 100 a-1to 100 a-N via power lines 2023-1 to 2023-N.

In this case, each disk device 100 a further has an electricity storageterminal 17 a via which to charge the electricity storage unit 13 a asshown in FIG. 16. FIG. 16 is a diagram illustrating schematically theconfiguration of the disk device 100 a. The electricity storage terminal17 a is electrically connected to the electricity storage unit 13 a ofthe host 200 a via the power line 2023 of a power line group 202 a.

A charging circuit 56 of each disk device 100 a can switch between afirst state and a second state as shown in FIG. 17. FIG. 17 is a diagramillustrating the configuration of circuitry related to the VCM 4 and SPM3. The first state is a state where the current path of the VCM 4 iselectrically cut off from the electricity storage unit 13 a via theelectricity storage terminal 17 a and the power line 2023. The secondstate is a state where the current path of the VCM 4 is electricallyconnected to the electricity storage unit 13 a via the electricitystorage terminal 17 a and the power line 2023. The charging circuit 56has a switch SW1, one end of the switch SW1 being electrically connectedto the current path of the VCM 4, the other end of the switch SW1 beingelectrically connected to the electricity storage terminal 17 a.According to a control signal received from the charge-discharge controlunit 55, the charging circuit 56 turns off the switch SW1 to switch tothe first state and turns on the switch SW1 to switch to the secondstate.

For example, the charging circuit 56 switches from the first state tothe second state during a seek time period when the head MH is made toseek. That is, the seek time period contains an acceleration period, aconstant speed period, and a deceleration period. The accelerationperiod is a period when the speed of the head MH is accelerated and is aperiod when the absolute value of the acceleration of the head MHexceeds a first threshold. The constant speed period is subsequent tothe acceleration period, is a period when the speed of the head MH canbe controlled to be almost constant, and is a period when the absolutevalue of the acceleration of the head MH is smaller than the firstthreshold. The deceleration period is subsequent to the constant speedperiod, is a period when the speed of the head MH is decelerated and isa period when the absolute value of the acceleration of the head MHexceeds the first threshold. At a first timing corresponding toswitching from the acceleration period to the constant speed period, thecharging circuit 56 switches from the first state to the second state.Thus, during the constant speed period, the charging circuit 56 cancharge the electricity storage unit 13 a with the VCM current I_(v) fromthe VCM 4. At a second timing corresponding to switching from theconstant speed period to the deceleration period, the charging circuit56 switches from the second state to the first state. Thus, the chargingcircuit 56 can finish charging the electricity storage unit 13 a withelectricity immediately before switching from the constant speed periodto the deceleration period.

Thus, as compared with the embodiment, the electricity storage unit 13 aneed not be included in each individual disk device 100 a, so that it ispossible to simplify the configuration and to reduce cost. Further, ascompared with the embodiment, power according to the back electromotivevoltage of the VCM 4 can be collected efficiently.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A disk device comprising: a head; a disk having arecording surface; a first motor that causes the head to seek along therecording surface; a first circuit that can switch between a first stateand a second state, the first state being a state where a current pathof the first motor is electrically cut off from a first electricitystorage unit, the second state being a state where the current path ofthe first motor is electrically connected to the first electricitystorage unit; a second motor that rotates the disk; and a second circuitthat includes a rectifying circuit connected to a current path of thesecond motor and can switch between a third state and a fourth state,the third state being a state where the rectifying circuit iselectrically cut off from a second electricity storage unit, the fourthstate being a state where the rectifying circuit is electricallyconnected to the second electricity storage unit.
 2. A disk devicecomprising: a head; a disk having a recording surface; a first motorthat causes the head to seek along the recording surface; a firstcircuit that can switch between a first state and a second state, thefirst state being a state where a current path of the first motor iselectrically cut off from a first electricity storage unit, the secondstate being a state where the current path of the first motor iselectrically connected to the first electricity storage unit; a powersupply circuit; and a third circuit that can switch between a fifthstate and a sixth state, the fifth state being a state where the firstelectricity storage unit is electrically cut off from the power supplycircuit, the sixth state being a state where the first electricitystorage unit is electrically connected to the power supply circuit. 3.The disk device according to claim 1, further comprising: a power supplycircuit; a third circuit that can switch between a fifth state and asixth state, the fifth state being a state where the first electricitystorage unit is electrically cut off from the power supply circuit, thesixth state being a state where the first electricity storage unit iselectrically connected to the power supply circuit; and a fourth circuitthat can switch between a seventh state and an eighth state, the seventhstate being a state where the second electricity storage unit iselectrically cut off from the power supply circuit, the eighth statebeing a state where the second electricity storage unit is electricallyconnected to the power supply circuit.
 4. A disk device comprising: ahead; a disk having a recording surface; a first motor that causes thehead to seek along the recording surface; and a first circuit that canswitch between a first state and a second state, the first state being astate where a current path of the first motor is electrically cut offfrom a first electricity storage unit, the second state being a statewhere the current path of the first motor is electrically connected tothe first electricity storage unit, wherein the first circuit switchesfrom the first state to the second state during a seek time period whenthe head is made to seek, wherein the seek time period includes: a firstperiod when absolute value of acceleration of the head exceeds a firstthreshold; and a second period subsequent to the first period and whenabsolute value of acceleration of the head is smaller than the firstthreshold, and wherein the first circuit switches from the first stateto the second state at a first timing corresponding to switching fromthe first period to the second period.
 5. The disk device according toclaim 4, wherein the seek time period further includes: a third periodsubsequent to the second period and when the absolute value ofacceleration of the head exceeds the first threshold, and wherein thefirst circuit switches from the second state to the first state at asecond timing corresponding to switching from the second period to thethird period.
 6. The disk device according to claim 2, wherein whenpower stored in the first electricity storage unit comes greater than orequal to a second threshold, the third circuit switches from the fifthstate to the sixth state.
 7. A disk device comprising a head; a diskhaving a recording surface; a first motor that causes the head to seekalong the recording surface; a first circuit that can switch between afirst state and a second state, the first state being a state where acurrent path of the first motor is electrically cut off from a firstelectricity storage unit, the second state being a state where thecurrent path of the first motor is electrically connected to the firstelectricity storage unit; and an electricity storage terminal that canbe connected to the first electricity storage unit via a power line,wherein the first state is a state where a current path of the firstmotor is electrically cut off from the first electricity storage unitvia the electricity storage terminal and the power line, and wherein thesecond state is a state where the current path of the first motor iselectrically connected to the first electricity storage unit via theelectricity storage terminal and the power line.